Imagine the Earth with a twin. Not a sci-fi planet in another galaxy, but a digital double built with satellites, sensors, and supercomputers. This twin could simulate floods before they happen, test how cities handle heatwaves, and reveal the carbon cost of our infrastructure.That is the promise of a digital twin of Earth. A living model that updates in real time, letting us test the future without breaking the present. And the race to build it is already underway.